Chlorinated anthraquinones

Anthraquinone can be brominated, chlorinated directly to the tetrachloro (I, 4, 5, 8-) stage, nitrated easily in the 1-position, but gives the 1,5-and 1,8-dinitro-derivalives on prolonged nitration the nitro groups in these compounds are easily displaced by neutral solutions of alkali sulphites yielding the corresponding sulphonic acids. Sulphonation with 20-30 % oleum gives the 2- 2,6- and 2,7-derivatives in the presence of Hg the 1- 1,5- and 1,8- derivatives are formed. 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

Use of mercuric catalysts has created a serious pollution problem thereby limiting the manufacture of such acids. Other catalysts such as palladium or mthenium have been proposed (17). Nitration of anthraquinone has been studied intensively in an effort to obtain 1-nitroanthraquinone [82-34-8] suitable for the manufacture of 1-aminoanthraquinone [82-45-1]. However, the nitration proceeds so rapidly that a mixture of mono- and dinitroanthraquinone is produced. It has not been possible, economically, to separate from this mixture 1-nitroanthraquinone in a yield and purity suitable for the manufacture of 1-aminoanthraquinone. Chlorination of anthraquinone cannot be used to manufacture 1-chloroanthraquinone [82-44-0] since polychlorinated products are formed readily. Consequentiy, 1-chloroanthraquinone is manufactured by reaction of anthraquinone-l-sulfonic acid [82-49-5] with sodium chlorate and hydrochloric acid (18). 

The performance of many metal-ion catalysts can be enhanced by doping with cesium compounds. This is a result both of the low ionization potential of cesium and its abiUty to stabilize high oxidation states of transition-metal oxo anions (50). Catalyst doping is one of the principal commercial uses of cesium. Cesium is a more powerflil oxidant than potassium, which it can replace. The amount of replacement is often a matter of economic benefit. Cesium-doped catalysts are used for the production of styrene monomer from ethyl benzene at metal oxide contacts or from toluene and methanol as Cs-exchanged zeofltes ethylene oxide ammonoxidation, acrolein (methacrolein) acryflc acid (methacrylic acid) methyl methacrylate monomer methanol phthahc anhydride anthraquinone various olefins chlorinations in low pressure ammonia synthesis and in the conversion of SO2 to SO in sulfuric acid production. 

In this reaction, three steps, ie, acylation, cyclization, and replacement of the chlorine atom by the hydroxyl group, take place simultaneously in concentrated sulfuric acid. In the course of cyclization 2,7-dichlorofluoran (31) may be formed as a by-product presumably through the carbonium ion (30) ihustrated as follows. The addition of boric acid suppresses this pathway and promotes the regular cyclization to form the anthraquinone stmcture. The stable boric acid ester formed also enables the complete replacement of chlorine atoms by the hydroxyl group. Hydrolysis of the boric acid ester of quinizarin is carried out by heating in dilute sulfuric acid. The purity of quinizarin thus obtained is around 90%. Highly pure product can be obtained by sublimation. 

Chloroanthraquinone [82-44-0] (41) is an intermediate for manufacturing vat dyes such as Cl Vat Brown 1. 1-Chloroanthraquinone is prepared by chlorination of anthraquinone-l-sulfonic acid with sodium chlorate in hydrochloric acid at elevated temperature (61). An alternative route from 1-nitroanthraquinone (18) using elemental chlorine at high temperature has been reported (62). 

An example of an anthraquinone thia2ole that has commercial importance is Cl Vat Blue 30 [6492-78-0] (167) (Cl 67110). This dye exhibits good fastness to light and chlorine. 

Sodium methylate acting on 2-chloroanthraquinone substitutes the methoxy group for chlorine and produces anion-radicals of the substrate (Shternshis et al. 1973). The study of kinetics has demonstrated that the amount of substrate anion-radical hrst increases and then sharply decreases. The inhibitor (p-BQ) decelerates the formation of anion-radicals. The rate of formation of 2-methoxy-anthraquinone also decreases. If anion-radicals are produced on the side pathway, the rate of formation of the end product on introduction of the inhibitor should not have decreased. Moreover, it should even rise because oxidation of anion-radicals regenerates uncharged molecules of the substrate. Hence, the anion-radical mechanism controls this reaction. 

A synthesis of the chlorinated angucycline antibiotic BE-23254 (1686), which was isolated from Streptomyces sp. A 23254, has confirmed the structure of this benz[a anthraquinone derivative (1644,1939,1940). Two detailed examinations of the rare Australian soil actinomycete Kibdelosporangium sp. uncovered a series of... 

Most of the previously identified 25 chlorinated anthraquinones are found in lichen and fungi (1). The newly discovered examples have a wider range of sources. Studies of the lichen Nephroma laevigatum from the British Columbia coast have identified the new anthraquinone, 7-chloro-l-O-methyl-co-hydroxy-emodin (2157), and the two novel hypericins, 7,7 -dichlorohypericin (2158) and 2,2, 7,7 -tetrachlorohypericin (2159) (1931), as well as 5-chloroemodin (2160), 5-c h I oro -1 - (9 - m e t h v I - o >- h yd ro x ye m od i n (2161), and 5-chloro-co-hydroxyemodin (2162) (1932). In addition to containing several known chlorinated anthraquinones, the Scandinavian fungus Dermocybe sanguinea has afforded the new 5,7-dichloroendocrocin (2163) (1933). The novel tetracyclic anthraquinones... 

The Streptomyces strain that produces celastramycin A (1212) has also yielded celastramycin B (2166) (1225). Another Streptomyces sp. has afforded bischloro-anthrabenzoxocinone ((-)-BABX) (2167), which has antibacterial activity and inhibits ligand-binding activity of liver X receptors (1937). An example of a rare chlorinated anthraquinone is anthrasesamone C (2168), which was characterized in the Japanese plant Sesamum indicum (1938). The angucycline-type marmycin B... 

Cohen PA, Towers GHN (1996) Biosynthetic Studies on Chlorinated Anthraquinones in the Lichen Nephroma laevigtum. Phytochemistry 42 1325... 

Cohen PA, Towers GHN (1997) Chlorination of Anthraquinones by Lichen and Fungal Enzymes. Phytochemistry 44 271... 

Prior to the discovery of a-sulfonation of anthraquinone, nitration was the only useful method for preparing a-substituted anthraquinones. The nitro group of a-nitroanthraquinones can be replaced in a manner similar to the sulfonic acid moiety, e.g., by chlorine atoms and amino, hydroxy, alkoxy, or mercapto groups. Reduction readily yields aminoanthraquinones. Nitration of anthraquinone has gained increasing importance because of environmental considerations, this method offering an economical alternative to a-sulfonation... 

Yang, Y. Z., Yang, W. S., Yang, F. L. and Zhang, X. W. (2005b), Electrooxidative degradation of an anthraquinone dye with in-situ electrogenerated active chlorine in a divided flow cell. Chin. J. Chem. Eng., 13(5) 628-633. 

Figure. 13.62 to 13.65 provide examples of chlorination reactions. In the first example, the commonly used agent FeCl3/Cl2 is employed for the chlorination of benzene and naphthalene rings. This method is not practical for the chlorination of anthraquinone. In this case the most important reaction is the tetrachlorination process shown in Fig. 13.63. 

Anthraquinone vat dyes containing a thia-zole ring include C.I. Vat Yellow 2, the synthesis of which is shown in Fig. 13.125. In this case, at least two approaches are possible. In the first, 2,6-diaminoanthraquinone is condensed with benzotrichloride in the presence of sulfur and the initial product is oxidized without isolation to give the target dye. Alternatively, the starting diamine can be chlorinated and converted to the corresponding dithiol (47). At this point condensation with benzaldehyde followed by oxidation (e.g. air or dichromate) gives the dye. 

The synthesis of the series of 2,4,5-amino-substituted derivatives of 1-phenoxy-anthraquinone (II) was accomplished by an exchange of chlorine or bromine atoms upon heating the corresponding 1-chloro- or 1-bromoanthraquinones in a phenol-phenoxide solution as well as by alkylation of 1-aminomethyl- or dimethylanthra-quinones using methyliodide.14... 

In special cases, chlorination is brought about by replacement of a sulfonic group by chlorine. This reaction is particularly important with anthraquinone compounds, but it is also known in the benzene series (see page 236). 

In the anthraquinone series, the a-sulfonic acids are characterized by the fact that the sulfo group is easily split out and replaced by nascent chlorine (also bromine). o-Chloroanthraquinone may be obtained in this way in excellent purity and yield. The /3-sulfonic acids also are capable of undergoing this reaction, but the reaction goes very slowly and not quantitatively because, besides replacement of the sulfo group by halogen, some replacement by hydrogen takes place also. 

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